A radio frequency (RF) communication system typically has a receiver and a transmitter. The transmitter includes a modulator to modulate a radio carrier with information or message and a power amplifier to emit the radio signal into open space. The receiver has RF stages that converts the received radio signal into some appropriate intermediate Frequency (IF) signal and a demodulator that converts the IF signal into a baseband signal and recovers the embedded modulating information in the received signal sent by the transmitter. In a multi-carrier system, the transmitted radio signal consists of a number of signals each of which has a sub-carrier frequency and carries independent information. The sub-carrier frequencies are spaced with a fixed constant such that the sub-carrier frequencies are orthogonal each other over a certain given symbol duration. The sub-carrier frequencies are usually symmetrical around the center frequency which is the radio carrier frequency for a radio multi-carrier signal or is 0 Hz or DC for a baseband multi-carrier signal.
Typically, the processing of the signals in the transmitter or receiver involves use of quadrature modulation or demodulation, respectively. For a quadrature demodulator, the received signal is down-converted into a complex baseband signal by in-phase (I) and quadrature (Q) mixers and the baseband signal is split into in-phase (I) and quadrature (Q) components to be processed separately in the respective I and Q channels. These two components are then usually filtered and converted into digital samples. For a quadrature modulator, a reverse procedure is carried out. In real systems, there are a number of problems associated with the processing of the signals, which result in poor performance. These problems include mismatch or imbalance in gain or group delays between the I and Q channels. As a result, the sub-carrier signals in a multi-carrier system may not completely satisfy the orthogonality over the symbol duration. These problems introduce cross-talks between the sub-carriers and distortion in the received or transmitted signals.
Therefore, there is a need to have an efficient technique to remove the adverse effects of the I-Q imbalances in a multi-carrier system.